In order to improve the characteristics of electric devices such as electric double-layer capacitors, methods of adding an additive to an electrolyte solution have been studied.
For example, in order to provide an electrolyte solution for electric double-layer capacitors having a low viscosity, a high electrical conductivity, a wide potential window, and excellent electrochemical stability, Patent Literature 1 proposes addition of a succinimide derivative having a specific structure to an electrolyte solution containing a quaternary ammonium salt as an electrolyte in a solvent.